It is known to use valve subassemblies placed down into a well using tubing, such as an uncased horizontal well that can be opened to fracture an oil producing formation to increase the flow of oil from the formation. These valve subassemblies or “subs” can comprise a ball valve seat mechanism that can receive a ball, which is placed into the tubing and travels down the tubing until it reaches the ball valve seat mechanism. Once the ball is seated in the valve seat, flow through the valve sub is cut off. The pressure of fracturing fluid injected into the tubing will cause the closed valve seat mechanism to slide a piston forward in the valve sub thereby opening ports in the wall of the valve sub to allow the pressure of the fracturing fluid penetrate into a production zone of a hydrocarbon bearing formation. The ball valve seat mechanism can be comprised of varying sized openings. Typically, a number of the valve subs are placed in series in the tubing at predetermined intervals in spacing along the well into the formation. The largest diameter valve seat is placed nearest the top of the well with progressively smaller diameter valve seats with each successive valve sub placed further along the tubing string.
In this manner, the furthest valve sub, the one having the smallest diameter opening can be closed by placing the matching sized ball into the tubing, which can pass through all of the preceding valve subs, each having larger diameters than the valve sub being closed, until the ball reaches its matching valve sub. One shortcoming of these known ball valve seat mechanisms is that the volume of fluid, and the rate of fluid flow, is constricted by the progressively decreasing diameter of the ball valve seat mechanism disposed in each of the valve subs, which becomes increasingly restricted with each successive valve sub in the tubing string. While the number of these valve subs can be as high as 23 stages, put in place with a packer system, the flow-rate that can be obtained through these valve subs is not high.
Another shortcoming of these known ball valve seat mechanisms is that the ball seats constrict the well bore with their presence. As such, full production and the ability to run conventional tools for production, work-overs and isolation testing are not possible. Current systems have balls and seats left in the well bore restricting production and plugging off sections of the liner with sand and balls. It is known to drill out balls and seats to achieve full production and access, however, the bore is still not full drift and is left with a restricted diameters inhibiting conventional tool use. In addition, these drill-outs are very costly and time consuming.
It is, therefore, desirable to provide a fracturing valve sub that overcomes the shortcomings of the prior art.